In certain types of medical emergencies a patient's heart stops working, which stops the blood from flowing. Without the blood flowing, organs like the brain will start being damaged, and the patient will soon die. Cardio Pulmonary Resuscitation (CPR) can forestall these risks. CPR includes performing repeated chest compressions to the chest of the patient, so as to cause the patient's blood to circulate some. CPR also includes delivering rescue breaths to the patient, so as to create air circulation in the lungs. CPR is intended to merely maintain the patient until a more definite therapy is made available, such as defibrillation. Defibrillation is an electrical shock deliberately delivered to a person in the hope of restoring their heart rhythm.
For making CPR circulate blood effectively, guidelines by medical experts such as the American Heart Association provide parameters for the chest compressions. The parameters include the frequency, the depth reached, fully releasing after a compression, and so on. Frequently the depth is to exceed 5 cm (2 in.). The parameters also include instructions for the rescue breaths.
Traditionally, CPR has been performed manually. A number of people have been trained in CPR, including some who are not in the medical professions, just in case they are bystanders in an emergency event. Manual CPR might be ineffective, however. Indeed, the rescuer might not be able to recall their training, especially under the stress of the moment. And even the best trained rescuer can become fatigued from performing the chest compressions for a long time, at which point their performance might be degraded. In the end, chest compressions that are not frequent enough, not deep enough, or not followed by a full release may fail to maintain the blood circulation required to forestall organ damage and death.
The risk of ineffective chest compressions has been addressed with CPR chest compression machines. Such machines have been known by a number of names, for example CPR chest compression machines, CPR machines, mechanical CPR devices, cardiac compressors and so on.
CPR chest compression machines hold the patient supine, which means lying on his or her back. Such machines then repeatedly compress and release the chest of the patient. In fact, they can be programmed so that they will automatically compress and release at the recommended rate or frequency, and can reach a specific depth within the range recommended by the guidelines.
The repeated chest compressions of CPR are actually compressions alternating with releases. The compressions cause the chest to be compressed from its original shape. During the releases the chest is decompressing, which means that the chest is undergoing the process of returning to its original shape. This process is not immediate upon release, and it might not be completed by the time the next compression is due. In addition, the chest may start collapsing due to the repeated compressions, which means that it might not fully return to its original height even if it had the opportunity.
Some CPR chest compression machines compress the chest by a piston. Some may even have a suction cup at the end of the piston, with which they lift the chest at least during the releases. This lifting may actively assist the chest in decompressing faster than the chest would accomplish by itself. This type of lifting is sometimes called active decompression.
Active decompression may improve air circulation in the patient, which is a component of CPR. The improved air circulation may be especially critical, given that the chest could be collapsing due to the repeated compressions, and would thus be unable by itself to intake the necessary air.